Drug Tunnels Have Feds Digging for Answers

U.S. Agents Can Spot the Passages, but the Brains Behind Them Prove Elusive

By

Tamara Audi

Jan. 31, 2013 10:12 p.m. ET

OTAY MESA, Calif.—The federal agents who spend their days hunting for tunnels used to smuggle marijuana from Mexico know the subtle signs of an illegal passageway hidden amid the labyrinth of warehouses in this border community just outside Tijuana.

They know large tunnels cost about $1 million apiece to build and can take up to nine months to finish. They know the suspected cartel kingpin allegedly behind the most sophisticated...